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// 工厂生成对象类public class OperationFactory{    public static OperationClass GetOperation(string operationType)    {        OperationClass opera = null;        switch (operationType)        {            case "+":                opera = new AddOperation();                break;            case "-":                opera = new SubOperation();                break;            case "*":                opera = new MulOperation();                break;            case "/":                opera = new DivOperation();                break;            case "sqrt":                opera = new SqrtOperation();                break;            case "squa":                opera = new SquareOperation();                break;            default:                 break;        }        return opera;    }}// 运算符基类public abstract class OperationClass{    public double NumA { get; set; }    public double NumB { get; set; }    public abstract double GetResult();        }// 加号类public class AddOperation : OperationClass{    public override double GetResult()    {        return NumA + NumB;    }}// 减号类public class SubOperation : OperationClass{    public override double GetResult()    {        return NumA - NumB;    }}// 除号类public class DivOperation : OperationClass{    public override double GetResult()    {        try        {            if (NumB.Equals(0))            {                throw new DivideByZeroException("分母为零");            }            return NumA / NumB;        }        catch (DivideByZeroException ex)        {            Console.WriteLine(ex);        }        return 0;               }}// 乘号类public class MulOperation : OperationClass{    public override double GetResult()    {                    return NumA * NumB;                }}// 开根号类public class SqrtOperation : OperationClass{    public override double GetResult()    {        return Math.Sqrt(NumA);    }}// 业务运用类public class OperationOutput{    public void Show()    {                    OperationClass ope;        do        {            Console.WriteLine("请输入正确的运算符： * / + - sqrt squa");            ope = OperationFactory.GetOperation(Console.ReadLine());        }        while (ope == null);                Console.WriteLine("请输入第一个数字");        ope.NumA = double.Parse(Console.ReadLine());        if (!(ope is SqrtOperation))        {                Console.WriteLine("请输入第二个数字");                ope.NumB = double.Parse(Console.ReadLine());        }                    Console.WriteLine("结果是：" + ope.GetResult());        Console.WriteLine();    }}

1）缺点：每新增一种操作，就需要修改 OperationFactory 类的 GetOperation(string operationType) 方法，这违法了对扩展开放，对修改封闭的原则。

2）可通过工厂模式、抽象工厂的方式得到适当改善，可通过反射彻底改善。